Painting method



.H. V. SCHWEITZER PAINTING METHOD Original" Filed Oct. 1, 1941 7 Sheets-Sheet 1 Jam * mvsmbn H. v. SCHWREITZERY I 2,434,125

PAINTING METHOD w Original Filed Oct. 1-, 1941 7 Sheets-Sheet 2 INVENTOR ATTORNEYS Jan. 6, 1948.

H. V. SCHWEITZER PAINTING METHOD Original Filed Oct. 1 1941. 7 Sheets-Sheet 4 w'uw ATTORNEYS Jan. 6, 1948. v, SQHWEHZER 2,434,125

' PAINTING METHOD I Original Fild Oct. 1 1941 7 Sheets-Sheet 5 I I M I mvsmon Q I 7 ATTORNEYS 1943- H. v; SCHWEITZER ,1

PAINTING METHOD I Original Filed Oct. 1 1941 7 Sheets-Sheet 6 Jan. 6, 1948.- H. v. SCHWEITZER PAINT ING METHOD Original Filed Oct. 1, 1941 7 Sheets-Sheet 7 INVENTOR Patented Jan. 6, 1 948 UNITED STATES PATENT OFFICE 413,173. Divided and this application 1943, Serial No. 493,836

8 Claims.

This invention relates to an improvement in the art of coating and, more particularly, to a method for painting large curved sheet metal surfaces, such as automobile hoods, fenders, panels, and the like. The subject matter of this application has been divided out of my copending application for Painting machine and method, Serial No. 413,173, filed October 1, 1941, now U. S. Patent No. 2,345,834.

It is the primary object of this invention to provide a method by which an automatic machine which will apply to large curved surfaces a substantially uniform coat of paint over the entire surface. I accomplish this object of my invention by revolving the article to be painted and by positioning the article so that, as it is revolved, the surface of the article generates an approximate geometric surface, usually that of a solid of revolution; I then move a coating device, i. e., a spray gun (hereinafter referred to as simply a gun), along a linear path substantially constantly spaced from the surface being generated, i. e., the surface being coated, the

July 8,

of the gun is varied from slow at the base of the cone to high near the apex. If the surface to be painted is a sphere, the gun is moved along a path concentric with the generating circle of the sphere, the speed of travel is varied from slow at the equator to high near the poles, and the angle of the gun is changed throughout its travel so that it is always normal to the surface of the sphere.

In actual use, not all articles can be painted by the above described method because their surfaces cannot fall on an approximate solid of revolution. However, in the many articles which can be painted by this method, the same general steps are followed even though the approximate solids of revolution, path and rate of gun travel,

gun being held at an angle substantially normal or perpendicular to the surface; and then, as the gun is then moved along its path, its speed of travel is controlled so that its several instant speeds are substantially inversely proportional to the circumferences of the circles described by the corresponding instant points to which the gun is normal. By so controlling the speed of travel of the gun in the manner described in this last step, I insure that each unit of area on the surface being painted is underthe gun (which delivers a substantially constant volume of paint) substantially the same length of time as any other unit of area on the surface being painted; thus, I obtain a uniform coat of paint on the article.

The foregoing description of my method in general terms may be amplified by describing its use on simple geometric surfaces. If the surface to be painted generates a cylinder, the gun is simply held normal to the cylinder and moved at a constant speed along a line parallel to an element of the cylinder. If the surface to be painted generates the area of a circle, 1. e., a disc, the gun is held perpendicular to the disc and moved along a line parallel to a radius of the disc, but the speed of travel of the gun is varied from slow at the perimeter of the disc to high near the center. If the surface to be painted generates a cone, the gun is held normal to the cone and moved along a path parallel to an element of the cone, but the speed of travel and angle of the gun cannot be readily calculated with mathematical nicety.

Although the foregoing method may be practised by hand, the invention is especially adapted to be practised by machines, such as the machine and its modifications as disclosed in the accompanying drawings and following specification.

Still other and further objects and advantages of this method will be apparent from the following specification, claims, and drawings of one embodiment of my invention. In the drawings:

Fig. 1 is an elevation, taken along the line l-l of Fig. 2, showing a painting machine which will operate according to this invention and also showing one gun at the top of its stroke and indicating the position of the gun at the bottom of its stroke and in intermediate positions.

Fig. 2 is a front elevation, partly broken away, of the machine shown in Fig. 1.

Fig. 3 is a sectional view taken along the line 33 of Fig. 2 to show a gun carriage, carriage track, and cam track.

Fig. 4 is an enlarged fragmentary detail view taken from Fig. 3 to show the operation of the gun carriage drive and gun tilting mechanism. In this view the moving parts shown in solid lines are not indicated in their relative positions when the gun is at the top of its stroke.

Fig. 5 is a view similar to Figs. 3 and 4 but partly diagrammatic, showing a modified gun tilting mechanism. In this view the moving parts shown in solid lines are not indicated in their relative positions when the gun is at the top of its stroke.

Fig. 6 is a fragmentary detail elevation taken along the line 66 of Fig. 1 to show the gun carriage drive control,

Fig. 7 is a fragmentary detail end section taken along the line 'I---'! of Fig. 6.

Fig. 8 is an enlarged detail view of the carriage drive timer cam.

Fig. 9 is an enlarged detail view of the spray gun timer cam.

In the drawings, in which like reference characters refer to like parts, I have shown, for simplicity of illustration, my machine set up for automatically painting automobile hood panels according to my method. Where moving parts of the machine are shown in solid lines, except in Figs. 4 and 5, the parts are in the position found when the spray gun is at the top of its stroke. The position of parts of the machine in other phases of the cycle of operation are indicated by the usual phantom showing, i. e., by light dot and dash lines. The directions employed in describing this invention are defined as follows: Forward denotes a direction toward the spindles, rear or rearwardly denotes a direction away from the spindles, outside denotes a direction away from the adjacent booth, and inside denotes a direction toward the adjacent booth.

Ihe hoods to be painted, I, are mounted on spindles 2 by means of suitable spacing and supporting frame members 3 and 4 carried by the spindles. Each of the spindles 2 are conveyed by a suitable conveyor system so that each spindle will remain for predetermined period before and aligned with the spray guns of the gun carriage booths 20 and I20. In the embodiment of this invention as shown in Figs. 1 and 2, the conveyor system is a conventional monorail system comprising an I-beam 5 along which evenly spaced hangers 6 are pulled by the conveyor chain I. This monorail system may conveniently be part of or associated with the conveyor system in the factory in which the painting machine is installed. By a suitable and conventional conveyor drive, not shown, the conveyor system is driven so that a hanger will remain at a given position for a known period of time and then the conveyor will be advanced until a succeeding hanger reaches the position occupied by the preceding hanger. Thus, the cycle of operation of the monorail conveyor system is made up of alternate stationary and advancing periods.

Each spindle 2 is mounted in a bearing 8 which permits the spindle 2 to be rotated in the hanger 6, by a spindle pulley 9. The spindle drive comprises a belt [0 driven on the drive pulley II and the idler pulley I2, as shown in Fig. 2. The drive pulley II is driven through a speed reducer I3 by a motor l4 mounted on the rail 5, as shown in Figs. 1 and 2. The drive pulley IIv and idler pulley I2 are mounted with respect to the conveyor system so that the spindle pulleys Swill be engaged by the belt ID as they are stationed before the gun carriage booths 20 and I20.

The main gun carriage booth 20 houses the gun carriage drive control, a gun carriage track, and gun carriage and is provided with a vertical slot 2| through which a gun arm extends. The booth 20 is positioned adjacent the conveyor 50 that the spray gun carried by the gun arm will be aligned with the axis of a spindle 2 during a stationar period of the conveyor travel. The auxiliary gun carriage booth I20 corresponds to the main booth 20, except that it does not house a gun carriage drive control. Consequently, it is provided with a vertical slot I2I in which a gun arm extends, the auxiliary booth I20 being positioned with respect to the conveyor system so 4 that a spray gun carried by its gun arm will be aligned with the axis of a spindle 2 during the stationary period of the conveyor system. The main booth 20 and auxiliary booth I20 are connected by conduit I6, which houses the shaft I'I connecting the carriage drive shafts of the two booths.

Operation of the conveyor system and spindle drive The unpainted automobile hoods I are loaded on the frames 4 at a suitable loading station (not shown). In the machine disclosed, the frame 4 positions the automobile hoods I so that their surfaces will lie approximately upon a solid of revolution, approximately defined as a cone with a rounded apex 'or as a paraboloid, when the spindle 2' is rotated on its axis. In the particular embodiment disclosed, three hoods I ma be hung on a single frame l. As is also shown in Fig. 1, edge and other portions of the hoods I may depart somewhat from the theoretical surface of a solid of revolution, such as the cone indicated by th element lines a, but such a minor deviation from the true surface of a solid of revolution has been found to. make no serious practical difference in the results obtained.

As the spindles 2 are periodically advanced toward the booth 20, the pulleys 9 will engage the belt IILcommencing to rotate the spindles 2, so that each spindle 2 will be rotating at substantially the desired speed when the spindles forward motionceases in front of the booth 20. While the conveyor drive is stationary, the spray gun of the booth 20 paints the surface of the hoods I in a manner to be described in greater detail below. Then the conveyor advances until the hoods which have received a first coat stop before the booth I20, where a second coat is applied. The spindles are then advanced beyond the belt I0 to a suitable unloading station, passing through a drying chamber if necessary.

In the embodiment disclosed, a two-coat machine is shown. Obviously, if but one coat is required, the auxiliary booth I 20 is not employed and, if more than two coats are required, additional auxiliary booths; may be added by means of suitable connecting; shafts and counter-shafts, the distance between the paths of travel of the spray guns inv the booths preferably being multiples (including 1) of the distances traveled by the spindles in, one period of advancement of the conveyor system- Gun carriage. and tilting mechanism In the embodiment shown in Figs. 1 to 4. of the drawings, booths 20 and I20 correspond, except thatthe main booth 20 houses the carriage drive control system. For clarity of illustration, the gun carriage, carriage drive, and gun tilting mechanism in the auxiliary booth I20 have been shown in detail in Figs. 3 and 4 and will be described in the following paragraphs. Corresponding parts will be found in the. main booth. (Parts in the main booth 20, where shown and indicated by reference characters, will be denoted by numerals from 22 to 4!, and corresponding parts in the auxiliary booth I20 will be denoted by numeralsfrom I22 to NH.)

In the auxiliary booth I20, a chassis I22v is housed. In order to permit an adjustment of the slope of the carriage travel, the chassis I22 is mounted on the pivot, I23 and held in its adjusted slop'e' by the adjustment screw I24. On the outside longitudinal rails I25 of the chassis are mounted the carriage guides I26.

A carriage I21 is mounted so that it may slide in the space between the guides I26. The carriage I21 carries four flange plates I28 which hold the carriage in the guides. upper end of the chassis I22 is a carriage driveshaft I29 (connected to the carriage drive connecting shaft I1 by a universal joint) which carries at its outside end, but inwardly of the guides I26, a carriage drive sprocket I30 which drives the carriage drive chain I3I extending between the drive sprocket I30 and the idler sprocket I32 mounted near the lower end of the chassis I22.

The carriage I21 is connected to the drive chain I3I by means of a connecting rod I33 pivotally connected to a block I34 carried by the chain I3I.

A gun arm I35 is journaled for longitudinal movement in a bearing I36 on the outside of the carriage I21 and extends through the slot IZI of the booth. At the forward end of the arm I35, outside the booth, a spray gun I31 is pivotally mounted so that, when the spindles 2 are held before the booth I20 in the stationary period of the chain I, the gun I31 will be aligned with the axis of a spindle 2. The rear end of the arm I35 within the booth is provided with a cam follower I38 which runs in the gun cam tracks I39 carried by the chassis I22. Integral with the gun I31 is a gun tilting crank arm I40 pivotally connected to the gun tilting connecting rod I4I which, in turn, is pivotally connected to the carriage I21. The gun I31 is of the automatic plunger type. Connected to the gun I31, therefore (but, for simplicity of illustration, not shown), is a flexible tube connected to a suitable source of paint supply, another tube is connected to a supplyof air for spraying paint, and a third tube is connected to a supply of air for operating the gun through a suitable gun control valve.

Operation of spray gun, gun carriage, and gun tilting mechanism The operation of the carriage drive, as shown in Figs. 3 and 4, is as follows: The shaft I29 is driven by the gun carriage drive control system, the operation of which is described in detail below, so that the chain I3I is driven at the desired speed and in synchronism with the conveyor system drive. As the chain I3I is driven around the drive sprocket I30 and the idler sprocket I32, the carriage I21 is pushed down and pulled up the track guides as the block I34 is carried around by the chain, as shown in Fig. 4, thus reciprocating the carriage I 21 in the guides I26. Because the block I34 pushes the carriage connecting rod I33 and the carriage I21 ahead of it but pulls the carriage after it, the guides I36 should extend below the idler sprocket I32, but need not extend so far above the drive sprocket I30, in order to support the carriage during the comparative dwell in its reciprocating motion which results when the block I34 passes around the sprockets I30 and I32. 1

As the carriage I21 reciprocates in its track, the gun arm I35 is carried with it and the cam follower I38 moves in the cam track I39. Between the points b and c, the center line of the cam track is parallel with the carriage track and the approximate element a of the solid generated by the revolved hoods. Between these points, the gun arm I35 will be fixed relative to the carriage and the gun I31 will be fixed relative to the gun arm. From the point to the point d, however, the cam track is curved forwardly. Thus, on the Journaled in the upstroke of the carriage, the gun arm I35 will be moved forward in its bearing I36 and, due to the crank arm I40 and tilting connecting rod I4I, the gun I31 will be simultaneously and gradually tilted downwardly, while the nozzle tip moves from the point 0' to d along its path of travel, as shown in Fig. 4. From the point at to the point e, which is at the top of the carriage stroke, the cam track I39 is parallel to the carriage track so that between the points d and e the gun arm I35 will remain in the position with respect to the carriage I 21 that was obtained at the point (1 and the spray gun I31 will reach the top of its stroke at e' in the tilted position obtained at the point (1'. On the downward stroke of the carriage the sequence of movements of the gun arm and spray gun will, of course, be reversed.

Assuming the operation of the carriage drive control to be as described and explained hereinafter, the painting operations of the machine disclosed in Figs. 1 to 4 may be best described by referring to Fig. 1. Fig. 1 is an end elevation of the main booth 20. As explained above, in so far as the carriage and associated mechanisms are concerned, their parts correspond in both the main and auxiliary booths 20 and I20. Therefore, the points in the paths of travel of the gun 31 and cam follower 38 correspond with those of the gun I31 and follower I38 and, consequently, are denoted by the same reference letters. The timing of the strokes of the gun 31 is so synchronized with the conveyor system that the period of advancement of the conveyor chain 1 occurs only while the gun 31 is near and at the top and/or bottom of its stroke in order that the gun 31 will be spraying only while the hanger 8 is stationary but while the spindle 2 is being rotated rapidly at a substantially constant speed by the belt I0. In other words, while a rotated spindle 2 is stationary before a carriage booth, the gun will spray during one upward or downward stroke. Ordinarily, the conveyor will advance a succeeding spindle into position between spraying periods of the gun, although, obviously, the spindle may remain in position before a carriage booth for any desired number of strokes of the spray gun.

Assuming that the machine disclosed advances the articles to be painted during the interim between each upward or downward stroke of the gun, in Fig. 1 the spindle 2 is advancing toward its position in front of the booth 20 and the spray gun 31 is at its comparative dwell while the chain block 34 passes over the drive sprocket 30. Then the carriage 21 accelerates rapidly and then commences to decelerate, the gun 31 approaching the point d at a high rate of speed. By the time the gun has reached the point d, the spindle 2 has become stationary before the booth 20 in line with the path of the gun 31 and the hoods I are being revolved at a substantially constant speed. When the gun reaches the point (1', it is normal to the surface of the approximate solid of revolution generated by the revolving hoods and the gun commences to spray. From the point d'to the point c, because the somewhat spherical surface, which the spray from the gun is covering, is increasing in area at an increasing rate, the speed of the gun along its path d'-e' is decelerated at a rate substantially inversely proportional to the increasing circumferences of the circles described by the points on the hood to which the gun is instantly normal. This deceleration is secured by the carriage drive control system and provides that a substantially even coat of paint will be applied to each unit of area on the hoods I.

lso, While the un is moving from d to C. it s. being moved rearwardly by the follower 38 in the cam track 39 and tilted upwardly by the crank arm 40 and tilting connecting rod 4! to maintain the gun substantially constantly spaced from and normal to the revolvin hoods I. From the point e, where the gun is normal to the point where the element of the approximate solid generated by the hoods changes from a curved line to a straight line, to the point ,1", where the gun is normal to the base of the said solid and where the spray is shut ofi, the gun continues to decelerate because the area of the hoods being covered by the spray is increasing. Because the gun will travel at less than its average speed at f, the gun is preferably accelerated in its travel from f to b, the point of comparative dwell at the end of its downward stroke, and then decelerated from b to f on its upward stroke. As the gun moves from f to I) back to -,f, where the spray is turned on, a succeeding spindle 2 is positioned in line with the gun by the conveyor system. The gun obviously follows the path of the downward stroke on its upward stroke and is accelerated from the point ,7" to near the point d at the same rate that it was decelerated on its downward stroke, the spray being shut off and the spindle 2 commencing to advance just after the gun passes the point d. As the gun approaches the point c, it decelerates to its comparative dwell at the end of its stroke, thus completing the cycle.

Since the shaft I! connects the drive shaft 29 of the booth 29 with the drive shaft I29 of the booth I29, and since a spindle 2 which is positioned in front of booth 20 during one stationary period of the conveyor system will be positioned before the booth I29 in a subsequent stationary period, hoods which receive a first coat from the gun 3! will receive a second coat in the same manner from the gun I31.

Construction and operation of modified gun positioning and tilting mechanism From the foregoing description of the machine shown in Figs. 1 to 4, it should be apparent that, due, to the fixed length of the crank arm and connecting rod in the gun tilting mechanism, the mechanism as shown in Fig. 4 is suitable for only a limited range of curves. Therefore, while the mechanism shown. is satisfactory for positioning and tilting the gun when painting simple curved surfaces, i. e., where the curvature is always in one direction. Thus, for example, in the hoods shown the curvature is alwaysdownward. The mechanism is not usually suitable, however, for painting pieces having a complex curvature, such as reentrant curves which may curve downwardly at some points and upwardly at others. While such reentrantly curved pieces could be painted with the mechanism shown in Fig. 4 by providing a gun arm with a plurality of guns, each with individual tilting cranks and connecting rods, for painting several differently curved areas, a preferred gun positioning and tilting device is shown in Fig. 5. The mechanism shown in Fig. 5 is operable to paint with one gun a reentrantly curved piece and is also adjustable to paint pieces having entirely different reentrant curves, though different cam tracks are required, of course, for each different type of reentrantly curved pieces. This result is obtained by providing means to tilt the gun independently of the means to position the gun (i, e., with respect to the carriage track) instead of means in which the tilting is dependent upon the positioning ofthe gun, as in Figs. ,1 to 4.

cated diagrammatically as 202 and the curved surface of the reentrantly curved piece to be painted is indicated diagrammatically as 20!. The booth'22il, having a gun arm slot 22!, houses a fixed vertical chassis 222 carrying guide tracks 225 in which the carriage 221, having flange plates 228, is reciprocated by the chain 23! through a suitable connecting link (not shown). The chain 23! is driven from a carriage drive shaft controlled by a suitable carriage drive control system. The carriage 227 is provided with a set of antifriction rollers 235 in which the gun arm, preferably telescopic, is journaled for horizontal movement. On the forward end of the arm 235 is pivotally mounted the spray gun 231; on the rear end of the arm 235 is mounted the cam follower 238 which runs in the gun positioning cam track 239. Fixed to or integral with the gun 23! is the tilting crank arm 24!) to which the gun tilting connecting rod 24! is pivoted in one of the several pivot holes in the crank arm 240. The connecting rod 24! is pivoted at its other end in one of the several pivot holes in the vertical T-bar 242 fixed to the forward end of the horizontal tilting cam rod 243. The tilting cam rod 243 is journaled in the set of anti-friction rollers 244 carried by the carriage 221 for horizontal movement parallel to the gun arm 235, The rear end of the cam rod 243 is provided with a cam follower 245 which runs in the gun tilting cam track 246. Near its rear end the cam rod 243 may be additionally supported by anti-friction rollers 24'! carried by the gun arm 235.

The operation of my modified gun positioning and tilting mechanism is as follows: As the carriage 22l i reciprocated in the track 226, the follower 23.8 in the track 239 will displace the gun arm 235 so that the pivot point of the gun 23'! will follow the path m,-n. Simultaneously, the tilting cam follower 245 running in the track 246 will displace the cam rod 243 horizontally and, through the T-bar 242, connecting rod 24!, and crank 243, will tilt the gun 23'! so that its nozzle will follow the path p--q and will always be normal to the surface being painted. It is obvious, of course, thatto apply an even coat of paint to each unit of area in the surface 20!, the speed of travel of the carriage 22'! must be accelerated or decelerated as the area being painted decreases or increases.

It is also apparent from Fig. v5, that by extending or shortening the telescopic gun arm 235 and changing the pivot points of the connecting rod 24! or employing longer or shorter connecting rods, the mechanism will be adjustable for a wide variety of differently curved pieces, although dif-- ferent cam tracks 239 and 245 may have to be employed for different pieces and the carriage drive control system may have to be retimed for different pieces. The method of determining the curvature of the cam tracks 239 and 245 will preferably be the same as that described above for determining the cam track I39.

Construction of carriage drive control System As is apparent from the above description of the operation of the spray guns and carriage drive for a machine which operates according to my invention, a carriage drive control system is an essential part of the machine when the speed of travel of the carriage is to be varied. A carriage drive control system for the machine illustrated in Figs. 1 to ii is shown in Figs. 6 t0 9 0f the drawings.

on the chassis 22 by means of an adjusting screw The motor 5!) drives the speed changing expansible pulley 52 which, in turn, drives the timer driving shaft 53 through the pulley 54. Mounted on the timer driving shaft 53 is a timer driving pulley 55 which drives the double expansible pulley 56 mountedon the rocking shaft 51 carried by the pivoted yoke 58. The double expansible pulley 55 is comprised of an axially shiftable center member 59 forming a driving V-belt pulley in combination with the first axially fixed member 60 and a driven V-belt pulley in combination with the second axially fixed member 5|. The double expansible pulley 55 drives the driven timer pulley 62 mounted on the input shaft of the speed reducer 33. The output shaft of the speed reducer 63 carries a sprocket 64 which drives the carriage Y drive shaft 29 through the drive shaft driving sprocket 65.

Also mounted on the carriage drive shaft 29 is a timer cam sprocket pinion 6B which drives a counter-sprocket gear 61 mounted on the counter- I 10 is such that the number of revolutions of the carriage drive shaft 29 sufficient to drive the carriage chain 3| completely around once will revolve the timer cam shaft 1| once. In other words, for every complete cycle of the block 34 from its position at the top of the carriage stroke, as shown in Fig. 6, around the idler sprocket 32 back to its position at the top of the carriage stroke, the timer cam shaft 1| will have made exactly one revolution.

Fixed to the timer cam shaft 1| is the carriage drive timer cam 12 which is engaged by the follower 13 carried by the yoke 58, the follower 13 being held in contact with the cam surface by means of the spring 14 extending from the yoke 58 to the chassis 22. Also fixed to the timer cam shaft 1| is the adjustable double on and off cam 15 which is engaged by the spring-pressed follower 16 which operates the valve 11 in the gun operating air line (not shown).

Operation of t e carriage drive control system The operation of the carriage drive control system for the machine illustrated in Figs. 1 to 4 is as follows: With the motor 50 driving the pulley 52, the driving diameter of the expansible pulley 52 is adjusted by means of the screw 5| until the speed of the carriage drive shaft 29 is such that it is in phase with the conveyor system, that is, the time required for one or any whole number of strokes of the carriage 21 will be precisely equal to the time required for one stationary period and one advancing period in the conveyor system j and the carriage will reach an end of its stroke preferably during the middle of the advancing period of the conveyor.

With the yoke 58 in the center position, as shown in solid lines in Figs. 6 to 8, no speed change is caused by the expansible pulley 56.- If the yoke is pivoted upwardly, however, the tension on the belt from the pulley 55 will push the center member 59 toward the driven member 6|, de-

creasing the driving diameter between the member 59 and the member 58 and increasing the speed of rotation of the double expansible pulley 56. At the same time, the driving diameter between the member 59 and the member 6| will be increased and thus further increasing the speed of the driven timer pulley 62. Thus, it will be seen that by pivoting the yoke 58 upwardly, the speed of the carriage drivingshaft 29 will be increased and the carriage 21 will be accelerated. Conversely, if the yoke 58 is pivoted in the opposite direction, the speed of the carriage driving shaft will be decreased and the carriage will be decelerated. Thus, upward movement of the yoke accelerates the carriage; downward movement decelerates the carriage, and, when the yoke is held in a fixed position, the speed of the carriage is constant, though the rate of speed depends upon the angle of the yoke. Consequently, with the carriage at the top of its stroke and the cam 12 engaged by the follower 13 at the point c", it is obvious that the shaft 29 is rotating at its average speed, because the yoke 58 is at its medial position, and, further, that the circle g represents the locus of points on the cam at which the shaft 29 will rotate at its average speed.

As is apparent from Fig. 8, as the cam 12 rotates, the follower will ride on the dwell adjacent the point e", (corresponding to the dwell in the carriage travel as the block 34 moves around the sprocket 35) and then will be rapidly raised 'upwardly, (consequently rapidly accelerating the carriage) until it reaches the point of maximum elevation as shown in the phantom lines of the drawing. (This position corresponds approximately to the position d of the path of the gun travel.) Then the follower tends to drop, decelerating the carriage, until the position of minimum elevation is reached, (corresponding approximately to the position f of the path of the gun travel). Then the follower 13 is rapidly raised, accelerating the carriage, until it approaches the dwell adjacent the point b, which is diametricall opposite the point e" (corresponding to the position of the gun at the bottom of its stroke). Since the cam 13 is symmetrical, on the upstroke the carriage will be rapidly decelerated and then accelerated until it approaches the top of its stroke, when it will rapidly decelerate as it reaches the dwell at the top of its stroke because the cam follower rapidly drops and then is raised until it drops into the dwell adjacent the point e". Fro-m the foregoing, it is apparent that the desired acceleration and deceleration of the carriage travel is obtained from the contour of the timer cam 12 and that the instant speed of the gun is approximatelypropor- -tional to theradial distance from the center of theshaft 1| to the point at which the'cam 12 is engaged bythe follower.

The on and off cam 15 is comprised of an .ofi plate 18 secured to the cam shaft 1| and an on plate 19 which maybe indexed around the shaft 1| with respect to the off plate 18 by means of the bolts located in the arcuate slots .8! of the plate 18 andthreaded in the plate 19.

:9, the cam follower will ride on the off surfaces of the'cam 15 until it engages the point d" of the on cam 19, where the follower 16 will rideup on the on surfaces of the cam, as shown in the phantom position,'opening the spray gunopcrating air valve 11 and turning the spray guns 31 and |31 on at the point 01 on the down stroke of the guns. The follower 16 will continue to ride on the on surfaces of the cam 15 until it reaches the point 1" of the o cam 18, where it will fall on the "off surfaces of the cam 15, shutting off the spray guns at the point f on the down stroke of the guns. As the shaft ll continues to rotate, the follower 16 will engage the point 1" on the on cam, turning the spray guns on at the point f on the upstroke of the guns and then will engage the point d" on the off cam, shutting the spray guns off at the point d of the upstroke of the guns, thereby completing the cycle. From the foregoing, it is apparent that the length of time the spray guns operate in any stroke is controlled by the length of the on surface of cam 15 and that relative phase of the stroke in which the guns operate is controlled by the indexing of the cam 15 on its cam shaft. Further, the type of spray gun control afforded by the on and on cam will permit many variations in the spray time with respect to the cycle of operation of the gun carriage. Thus, if it is desirable to have the guns turn on and oil several times during the cycle, the number of on surfaces in the cam should be increased; or, if it is desired to have the guns spray only during down strokes, for example, only one on" surface need be employed, or the length of the on surfaces may be cut in half and the speed of the cam shaft doubled with respect to the speed of the shaft of the carriage timer cam.

From the foregoing, it is apparent that this invention is not limited to the operation of the machine and modifications disclosed but may be practised by hand or by machines which will operate to apply paint to articles carried by a constantly moving conveyor system. This invention is not limited, therefore, to the specific embodiments disclosed, either in whole or in part, but is limited only by the appended claims.

What is claimed is:

1. The method of coating an article having a substantial portion of its surface approximating that of a solid of revolution generated by a curve extending through points varying in distance from the axis of revolution comprising the steps of revolving the article to be coated about said axis, applying a coating to successive integers of the surface of the article by moving a coating means along a linear path adjacent the article and having a component extending in the direction of said generating curve, and changing the speed of the coating means along its path substantially inversely proportionately to the change in area of the successive integers of the surface being coated while delivering a substantially constant volume of coating material from said coating means.

2. The method of coating comprising the steps of positioning an article, which has a surface which will approximately coincide with the surface of a solid of revolution generated by a curve extending through points varying in distance from the axis of revolution, on a spindle having an axis coinciding with the axis of the solid of revolution, revolving the spindle, applying a coating to successive integers of the surface of the article by moving a coating means along a linear path adjacent the article and having a component extending in the direction of said generat ing curve, and changing. the speed of the coating means along its path substantially inversely pro- 3. The method of painting comprising the steps of positioning an article on a spindle so that a majority of its surface will approximately coincide with the surface of a solid of revolution having circumferential areas of varying radii when the spindle is revolved, revolving the spindle, and moving a paint spray gun along a linear path substantially constantly spaced from the approximate surface generated by the revolved article, while maintaining said spray gun substantially normal to the surface generated.

4. The method of painting as defined in claim 3 in which the step of moving the gun includes moving the gun at a changing speed substantially inversely proportionately to the changing circumferences 0f the circles, on the solid of revolution, described by the points to which the gun is normal.

5. The method of painting an article having a substantial portion of its surface approximatin that of a solid of revolution generated by a curve extending through points varying in distance from the axis of revolution comprising the steps of moving a spray gun along a linear path, moving the surface of the article at a substantially constant angular rate of speed about its axis through a plane in which the path of said gun lies said path being substantially equidistant along its length from the intersection of said plane by said article, maintaining said gun approximately normal to said surface and simultaneously spraying successive integers of said surface while moving said gun along its linear path, and changing the speed of said gun along its path as the successive integers of said surface change in area, the rate of change of the gun speed being substantially inversely proportional to the rate of change in area of such successive integers.

6. The method of coating an article having an exterior surface which approximates at least a segment of a surface of a solid of revolution having circumferential areas of varying radii comprising the steps of supporting the article so that the surface to be painted will substantially coincide with the surface of a solid of revolution, revolving said article about the axis of such solid of revolution at a substantially constant rate of speed, spraying coating material from a spray gun, moving said spray gun along a linear path, said path being parallel to a line faired through the element of such solid of revolution when the element lies in the plane determined by the path and the axis of the solid of revolution and the speed of said gun along said path being such that each unit of area of the surface to be painted receives a substantially uniform volume of coating material from said spray gun.

'7. The method as defined in claim 6 including the steps of simultaneously moving said gun transversely to said path to maintain said gun substantially constantly spaced from the surface of such solid of revolution when such solid of revolution has a curved element and tilting said gun to maintain said gun substantially normal .to such solid of revolution.

8. The method of coating generally coniform surfaces, which consists in imparting rotation to the coniform surface while directing a spray of coating material against the rotating generally coniform surface at the largest diameter thereof, and bringing about relative movement between said surface and said spray in the direction of the axis of said surface at a rate gradually acceler- 13 ated in degree corresponding to the graduality of the decrease in diameter of said surface, thereby to gradually decrease the amount of applied spray accordingly as the area to be sprayed decreases and provide a spray coating of substantially uniform thickness throughout the area to be spray coated.

HOWARD V. SCHWEITZER.

REFERENCES CITED The following references are of record in the file of this patent:

Number UNITED STATES PATENTS Name Date Whitaker Oct. 18, 1932 Burdette July 13, 1937 Johnson Apr. 24, 1934 Blake June 5, 1928 Brackett June 15, 1937 Stewart June 7, 1938 Schweitzer Apr. 4, 1944 Rose Feb. 20, 1934 Wagner Sept. 15, 1942 

